Vehicles powered by an internal combustion engine typically include a starter assembly and an alternator assembly. The starter assembly is used to start the engine when operation of the engine is desired. The starter is typically coupled to a bottom side of the engine. The starter assembly includes an electric motor and a drive mechanism. The electric motor is energized by a battery upon closing of an ignition switch. The drive mechanism meshingly engages a flywheel of the engine to transfer the torque of the electric motor to a crankshaft of the engine. Rotation of the crankshaft causes the engine to start, at which point the electric motor is de-energized and the drive mechanism is disengaged from the flywheel.
The alternator assembly associated with a typical internal combustion engine is a separate assembly from the starter assembly, and is used to generate electricity for charging the above-mentioned battery and for powering vehicle accessories, such as lighting. The alternator assembly is typically mounted at the front of the engine by a bracket or the like. The alternator assembly includes an electric machine configured as a generator and including a rotor and a stator. The rotor is connected to the engine crankshaft by a belt-drive system including pulleys and at least one endless belt. Operation of the engine turns the belt, resulting in rotation of the rotor. Rotation of the rotor relative to the stator generates electricity.
Instead of a separate starter assembly and alternator assembly, some vehicles include a belt alternator-starter assembly (“BAS”), which is a single unit that combines the functionality of a starter assembly and an alternator assembly. The BAS is typically positioned at the front of the engine in the typical position of an alternator. The BAS is connected to the engine crankshaft by a belt-drive system that includes pulleys and at least one endless belt. The BAS includes an electric machine having a stator and a rotor. The electric machine is selectively operable as an electric motor or a generator.
In order to start the engine, the BAS is operated as an electric motor and is connected to the battery, which causes the rotor to generate a torque. The belt-drive system transfers the torque generated by the BAS to the engine crankshaft to rotate the crankshaft and to start the engine.
After the engine is started, the BAS is operated as a generator/alternator. When configured as a generator the belt-drive system transfers torque generated by the engine crankshaft to the rotor, which causes the rotor to rotate relative to the stator and to generate electricity. The generated electricity is used to charge the battery and to power vehicle accessories, such as lighting.
When starting the engine with the BAS, the electric machine is subject to a high torque/low angular velocity load; however, when the BAS is operated as a generator the electric machine is subject to a low torque/high angular velocity load. To make the BAS operate effectively in both situations, the electric machine is typically made to be larger and more powerful than the electric machine of a typical alternator, since the electric machine of a typical alternator would not be powerful enough when operated as an electric motor. As a result of having a larger and more powerful electric machine, the typical BAS is more expensive to manufacture than the typical alternator assembly. Accordingly, it would be desirable to reduce the manufacturing cost a BAS.